1. Field of the Invention
The present invention generally relates to a polishing method and apparatus. In particular, the present invention relates to a polishing method and apparatus for semiconductor wafers of Si, GaAs, InP, etc. and substrates, such as quartz substrates and glass substrates with a plurality of island-like semiconductor regions formed on the surfaces thereof.
2. Related Background Art
With progress in microfabrication of semiconductor devices, there are needs for highly precise planarization of outer surfaces of semiconductor wafers of Si, GaAs, InP, etc. and substrates, such as quartz substrates and glass substrates on the surface of which a plurality of island-like semiconductor regions are formed. Further, global planarization of the outer surfaces of substrates is also demanded due to the emergence of SOI wafers and the necessity for three-dimensional integration.
In addition to such global planarization of substrates, chemical mechanical polishing (CMP) devices, for example, are conventionally known as a type of planarization techniques capable of micro-planarization.
FIG. 16 is a schematic sectional view showing the main configuration of a chemical mechanical polishing (hereinafter referred to as “CMP”) apparatus 1000. The CMP apparatus 1000 has a wafer chuck 1010 for holding a wafer W as a work with its surface to be polished facing down, and a polishing table 1020 which is placed so as to face the wafer W held on the wafer chuck 1010 and to which a polishing pad P formed of, e.g., polyurethane and having a diameter greater than that of the wafer W is attached. The CMP 1000 is further provided with an abrasive material supply means 1030 for supplying an abrasive material (slurry) S onto the polishing pad P.
In the CMP apparatus 1000, the wafer W and the polishing pad P are rotated by a driving means (not shown) in the direction indicated by the arrows, with the surface of the wafer W to be polished being in contact with the polishing pad P and a predetermined processing pressure being applied to the wafer W; at the same time, the abrasive material S is dripped onto the polishing pad P from the abrasive material supply means 1030 to polish the surface of the wafer W to be polished. Regarding the driving of the wafer W and the polishing pad P, when the rotating speeds (RPMs) of the wafer W and the polishing pad P are equalized, the linear speed of the polishing pad P becomes constant at an arbitrary position on the wafer W, which is desirable for global planarization. However, the grid-like groove pattern in the surface of the polishing pad P is transferred to the polished surface of the wafer W, thus making it impossible to achieve micro-planarization. In view of this, it is common practice to perform polishing with a deviation of several percent between the rotating speeds of the wafer W and the polishing pad P.
As shown in FIG. 17, on the surface of the substrate be polished, such as a wafer, there is arranged, in addition to a device pattern DP for forming a semiconductor device, a mark for measurement (hereinafter referred to as the “measurement mark”) (alignment mark) AM for effecting positioning on an alignment detection system for an overlay inspection device, an exposure device, etc. As shown in FIG. 17, also on the measurement mark AM, there is formed a film C in which an insulating film, a dielectric, etc. are stacked together. During the polishing process, the portion of the film C on the measurement mark AM is polished simultaneously with the portion of the film C on the device pattern DP. Here, FIG. 17 is a schematic sectional view showing how the device pattern and the measurement mark are arranged on the surface of the wafer to be polished.
Generally speaking, a device pattern to be planarized by a CMP apparatus is a minute pattern of 1 μm or less, and, in the current state of mass production, 0.9 μm or less, whereas the size of measurement mark is approximately 30 μm to 300 μm, and the line width used is approximately 1 μm to 30 μm. Further, in a CMP apparatus, polishing is effected with a viscoelastic polishing pad, such as a polyurethane pad, so that, due to deformation of the polishing pad during polishing, the portions where the projections and depressions are not dense are not polished flat, resulting in so-called dishing, erosion, and thinning. Thus, in the film portion on the measurement mark, slight projections and depressions are allowed to remain even after the planarization by the CMP apparatus, and these residual slight projections and depressions make it possible to perform alignment measurement and overlay inspection measurement.
However, the configuration of the measurement mark for alignment measurement and overlay inspection measurement is under the influence of dishing, erosion, and thinning, and the size of the measurement mark is relatively large, in particular, in width, as compared with the device pattern, which leads to a difference in the peripheral pattern density, resulting in over-polishing or the like. As a result, the configuration of the measurement mark becomes asymmetrical, which leads to a deterioration in accuracy in alignment and overlay inspection.
The actually used system for the alignment detection system for the overlay inspection device, exposure device, etc. is mostly of a bright visual field image processing type, which is constructed as shown in FIG. 18. An alignment detection system 2000 detects a measurement mark AM formed on a wafer W by using the imaging action of the optical system, and forms its image on a CCD 2020 serving as the imaging device through an optical system 2010, and various signal processings are performed on the video signal, thereby performing alignment measurement or overlay inspection. Here, FIG. 18 is a schematic block diagram showing the construction of the bright visual field image processing type alignment detection system 2000.
The most needed imaging performance in the optical system of the alignment detection system is image symmetry. However, when, as shown in (a) of FIG. 19, the film C on the measurement mark AM is asymmetrical, lights A through D vertically impinging on the measurement mark AM are reflected at different angles, and the reflection lights A′ through D′ effect imaging on the CCD to undergo photoelectric conversion, becoming a video signal as shown in (b) of FIG. 19. At this time, the reflection angles of the lights reflected from the right and left sides of the measurement mark AM differ, so that the video signal is also asymmetrical, which leads to distortion, resulting in positional deviation. This leads to a deterioration in alignment accuracy and overlay inspection accuracy. Here, (a) of FIG. 19 is a schematic sectional diagram showing how reflection lights are reflected at different angles by the measurement mark, and (b) of FIG. 19 is a diagram showing the video signal obtained through photoelectric conversion of the reflection lights shown in (a) of FIG. 19.
In this way, in the conventional CMP apparatus, the film on the measurement mark is polished asymmetrically, so that the positioning accuracy deteriorates in the alignment detection system for the overlay inspection device, exposure device, etc.
In view of this, the inventor of the present invention has proposed a method according to which asymmetrical polishing of the film on the measurement mark is prevented through control of the rotating speed of the semiconductor substrate and/or the polishing pad (see, for example, Japanese Patent Application Laid-Open No. 2002-25958).
However, due to the recent rapid progress in the microfabrication technique for semiconductor devices, it has become impossible to meet the requisite level of alignment accuracy and overlay inspection accuracy even through polishing while controlling the rotating speed of the semiconductor substrate and/or the polishing pad. In other words, while the control of the rotating speed of the semiconductor substrate and/or the polishing pad makes it possible to mitigate asymmetrical polishing of the film on the measurement mark, it does not enable the film on the measurement mark to be polished symmetrically but allows generation of slight asymmetric diversity.